Method for the status analysis of a subscriber loop to support broadband telecommunication services

ABSTRACT

A method for analyzing the status of a subscriber loop belonging to an access network portion of a fixed network infrastructure, the subscriber loop not supporting a broadband service wherein the access network portion includes further subscriber loops, a set of which support broadband services. The method includes the steps of collecting attenuation measures associated with said set of subscriber loops supporting said broadband services; and processing said attenuation measures to obtain an estimation of a maximum bit rate that can be offered on the subscriber loop to be analyzed.

CROSS REFERENCE TO RELATED APPLICATION

This application is a national phase application based onPCT/IB2006/003796, filed Dec. 29, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally refers to the provision of broadbandtelecommunication services. In particular, the present invention refersto a method for designing a broadband telecommunication service based ona technology of the xDSL (“generic Digital Subscriber Line”) type for asubscriber loop on which nowadays only traditional POTS or ISDN (“PlainOld Telephone Service” or “Integrated Services Digital Network”)telephone systems are provided.

2. Description of the Related Art

The exponential increase in the popularity of the Internet and ofrelated data services has prompted service providers in the PublicSwitched Telephone Network (PSTN), to seek new technologies to deliverhigh speed data services to their customers. One solution is provided byDSL (Digital Subscriber Line) technologies. Several DSL technologiesoffer high speed services over existing copper facilities commonlyreferred to “subscriber loops”. Such technologies include ADSL(“Asymmetrical Digital Subscriber Line”); HDSL (“High-bit-rate DigitalSubscriber Line”); RDSL (“Rate Adaptive Digital Subscriber Line”); SDSL(“Symmetric Digital Subscriber Line”); and VDSL (very High-speed DigitalSubscriber Line”). These DSL or similar technologies are collectivelyknown as “xDSL” services.

A problem encountered in the provision of xDSL services is thatsubscriber loops have largely been neglected from a technology upgradeperspective. Existing subscriber loops and the structure of the copperdistribution network were originally designed for narrow band voicetelephony and not to support high speed data services. Consequently, theelectrical characteristics of the cables and subscriber loops set limitsto the provision of broadband services: for example, many subscriberloops include wire gauge changes and bridged taps (unused extensionlines) which limit the available bandwidth, limiting the performance ofthe loops with respect to the delivery of an xDSL service.

U.S. Pat. No. 6,266,395 discloses a method and an apparatus forsingle-ended qualification of subscriber loops for xDSL services. Themethod involves first screening a subscriber loop database fordisqualifying devices or services, associated with that loop, which areincompatible with xDSL services. If none are found, a set ofpredetermined electrical characteristics of the subscriber loop arederived from information in the database, or directly measured usingtest equipment at a central office end of the subscriber loop. Theelectrical characteristics are used to calculate an available bandwidthfor xDSL services on the subscriber loop.

In W0 02/21742 a system is disclosed that is able to predict theperformance of a DSL line on an already installed telephone loop. Thesystem obtains a topologic description of the already installedtelephone loop and through it, it identifies an equivalent loop.Afterwards, the system determines DSL performance for the equivalentloop. From DSL performance of the equivalent loop, the system predictsDSL performance for the already installed telephone loop.

SUMMARY OF THE INVENTION

The Applicant has noted that each cable section composing a subscriberloop of a Copper Access Network, due to its difference with respect toother sections (in terms of length, structure, coating, type ofinsulating material among the subscriber loops composing it, loop numberand diameter) can be seen as a transmission channel with its ownelectric and physical characteristics. In general, such transmissionchannel can introduce on a xDSL signal crossing it an attenuation, aphase distortion and a noise level that are different from thoseintroduced by another transmission channel.

Moreover, impedance discontinuities found along a subscriber loop on itspath between central station and subscriber premises, due for example tojunctions of different lengths, cable terminations in network elements(ex. permutators, cabinets and distribution points) can have an evensignificant effect on the level and/or the quality of the xDSL signalreceived by the subscriber set to such loop.

From what has been stated above, it can be assumed that a Networkoperator could be able to obtain an adequate estimation of the maximumbit rate that can be obtained on a subscriber loop (for exampledepending on certain noise conditions), only having an accurateknowledge of all characteristics (cable type, diameter, etc.) ofindividual cable lengths composing it.

The Applicant has however noted that, in the majority of cases, theNetwork operator has not available a reliable and complete descriptionof his own network in terms of transmission characteristics ofindividual cable sections composing it, since these information aregenerally unavailable on a local basis but only on a statistical basisat national or regional level.

The Applicant therefore has noted that, for a Network operator thatwishes to provide a broadband service, based for example on a technologyof the xDSL type, on a specific subscriber loop of his own copper accessnetwork, there is the need of adequately estimating the quality ofservice that can be offered on such particular loop, expressing suchquality in terms of maximum bit rate that can be reached on the loopitself.

The Applicant has observed that, in order to adequately estimate themaximum bit rate that can be reached on a specific subscriber loop of acopper access network, it is enough to use attenuation measures of theDELT (Dual Ended Line Test) type associated with xDSL services alreadydeployed in portions of network common to the subscriber loop to bequalified.

In the present description, the term “common network portion” for two ormore subscriber loops means the network portion composed of the set ofnetwork cables and equipment common to said two or more subscriberloops.

In the present description, the term “attenuation measures of the DELTtype” means the attenuation measures that terminal equipment, forexample two xDSL modems, one placed in the Operator central, the otherone placed in the subscriber premises, estimate and can exchange,through messages containing information dealing with the line status,including the cable sections, as well as perceived by each of the twoterminations.

The attenuation measures of the DELT (Dual Ended Line Test) type ofinterest can be those provided by the ITU-T G.997.1 standard “Physicallayer management for digital subscriber line (DSL) transceivers”, inparticular attenuation signal and attenuation loop related to uplink anddownlink.

In the present description, the term “attenuation signal of a xDSL line”means the difference between transmitted power and received power,related to uplink or downlink of the line, measured on xDSL carriersused when transmitting.

In the present description, the term “attenuation loop” means thedifference between transmitted power and received power, related touplink or downlink of the line, measured on all carriers of the xDSLspectrum.

Alternatively, the same attenuation measures can be obtained by usingequipment not complying with the G.997.1 standard and such as toimplement algorithms of the proprietary type for estimating theattenuation measures.

A first aspect of the present invention refers to a method for analysingthe status of a subscriber loop belonging to an access network portionof a fixed network infrastructure, said subscriber loop not supporting abroadband service, said access network portion comprising furthersubscriber loops, a set of which supporting broadband services, saidmethod comprising the steps of:

-   -   collecting attenuation measures associated to said set of        subscriber loops supporting said broadband services; and    -   processing said attenuation measures to obtain an estimation of        a maximum bit rate that can be provided on said subscriber loop        to be analysed.

A second aspect refers to a system for analysing the status of asubscriber loop belonging to an access network portion of a fixednetwork infrastructure, said subscriber loop not supporting a broadbandservice, said access network portion comprising further subscriberloops, a set of which supporting broadband services, said systemcomprising:

-   -   a module configured for collecting attenuation measures        associated to said set of subscriber loops supporting said        broadband services; and    -   a module configured for processing said attenuation measures to        obtain an estimation of a maximum bit rate that can be provided        on said subscriber loop to be analysed.

A further aspect of the present invention refers to an informationproduct that can be loaded in the memory of at least one electronicprocessor and comprising portions of software code for carrying out theprocess according to the invention when the product is run on aprocessor: in this context, such term should be considered whollyequivalent to the mention of a computer readable medium comprisinginstructions for controlling a network of computers in order to carryout a process according to the invention. The reference to “at least oneelectronic processor” is aimed to underline the chance of performing thesolution according to the invention in a de-centralised context.

Further preferred aspects of the present invention are described in thedependent claims and in the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics and advantages of the present invention will beclear from the following description of an embodiment, provided as anon-limiting example, with reference to the enclosed drawings, in which:

FIG. 1 is a schematic representation of a fixed network infrastructureand of suitable systems for storing information and measures related tothe network infrastructure itself;

FIG. 2 is a schematic representation of an access network of the fixednetwork infrastructure shown in FIG. 1;

FIG. 3 shows a flow diagram related to the analysis method of the statusof a subscriber loop according to the invention;

FIG. 4 shows a flow diagram related to a step of the analysis methodaccording to the invention; and

FIG. 5 shows a flow diagram related to a further step of the analysismethod according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, the analysis method according to the inventionoperates on a fixed network infrastructure 1 comprising: an accessnetwork 2, central apparatus 3 (permutators, multiplexers, etc.) locatedin Network operator premises and equipment subscriber 4 or CPE(“Customer Premises Equipment”) (for example telephones, gateways, xDSLmodems, etc) located in subscriber premises.

The access network 2, for example made of copper, includes a pluralityof cables 6 each guaranteeing an electric continuity between centralapparatus 3 and subscriber equipment 4.

With reference now to FIG. 2, each central apparatus 3 can for exampleinclude a telecommunication central station 8, comprising a first branchand flexibility point composed of a central permutator 9 (MDF: MainDistribution Frame) in which the subscriber loops (“copper pairs”) 7converge, connected to that telecommunication central station, andmultiplexers 10, so-called DSLAM (“Digital Subscriber Line AccessMultiplexer”), connected through the central permutator 9 to thesubscriber loops 7 and configured for managing the data traffic from thesubscriber loops 7. In particular, the central permutators 9 areflexibility elements of the access network 2 through which the Networkoperator performs the connection between the remote subscriber equipmentand the specific central apparatus responsible for delivering theservice required by the remote subscriber equipment.

Each cable 6 comprises a primary section 6 a that connects the centralpermutator 9 to one or more second branch and flexibility pointsimplemented by a cabinet 11. Each primary section 6 a includes theplurality of subscriber loops 7, a set of which supporting broadbandtransmission systems, for example of the xDSL type. The portions ofprimary section 6 a connected to the central permutator 9 generally havea high transmission potential since the subscriber loops composing themare on the order of thousands, while the portions of primary section 6 aconnected to each cabinet 11 have a lower transmission potential, sincethe subscriber loops composing them are on the order of hundreds.Permutators 9, primary sections 6 a and cabinets 11 compose theso-called primary access network.

Each cable 6 also comprises a plurality of secondary sections 6 b (alsowith a more and more decreasing transmission potential along thesubscriber equipment 4 direction) that connect cabinet 11 to networkdistribution points 12. Specifically, each cabinet 11 can be connectedto many distribution points 12. The set of distribution points 12connected to a single cabinet 11 realises the so-called “cabinet area”13. Cabinets 11, secondary portionshs 6 b and distribution points 12realise the so-called secondary access network.

From each distribution point 12 tens of individuals subscriber loops 14branch towards the subscriber equipments 4, each loop reaching thepremises of the various users jointing a respective Domestic NetworkTermination, not shown in FIG. 2. Downstream of such Domestic NetworkTermination, the “subscriber system” develops, comprising the homewiring (namely the set of cables inside the subscriber premises) and thesubscriber equipment 4. The Domestic Network Termination realises theseparation element between Operator network and subscriber system.

The copper access network 2 shown in FIG. 2 can also have somevariations, mainly due to system and/or cost needs.

For example, each distribution point 12 can be connected to therespective permutator 9 without using a cabinet 11. In this case, theaccess network 2 is called “rigid” as opposed to the above-describedflexible access network model that provides for the presence of cabinets11.

A second variation of the above described access network 2 provides thatcables 6 connected between the permutator 9 and distribution points 12cross many cabinets 11.

The analysis method of the present invention can be applied to bothabove described variations of the access network 2. In particular, inthe second variation, the cabinet 11 that will be taken as referencecabinet is the one directly connected to the distribution point.

Specifically, the analysis method according to the invention allows aNetwork operator to be able to qualify:

-   -   in a flexible network, all lines of an cabinet area where there        are at least two network distribution points of the broadband        type equipped with validated attenuation measures of the DELT        type;    -   in a rigid network, all network distribution point lines of the        broadband type equipped with validated attenuation measures of        the DELT type.

In the present description, the term “network distribution point of thebroadband type” will mean a network distribution point to which at leastone subscriber loop supporting a service of the xDSL type is connected.

Moreover, in the present description, the term “network distributionpoint of the broadband type equipped with validated attenuation measuresof the DELT type” will mean a distribution point to which xDSL lines areconnected, for which attenuation measures of the DELT type areavailable, that are validated and possibly corrected according to aseries of procedures described herein below in the present description.

The analysis method of the present invention can be applied to theaccess network 2 and its variations provided that a set of attenuationmeasures of the DELT type have previously been acquired on subscriberloops deployed in a network that already supports a service of the xDSLtype (defined as “xDSL lines” herein below in the present description),for both uplink and downlink of the loops themselves, and suitablystored in a measure database 15 associated with the fixed networkinfrastructure 1 as shown in FIG. 1.

A method for acquiring and storing such attenuation measures that can beused with the analysis method of the present invention is for exampledescribed in WO 05/094001 A1. When acquiring and storing suchattenuation measures, a series of conditions should be complied with,namely:

a) for each xDSL line, in both uplink and downlink, the previouslydescribed attenuation measures of the DELT type should be acquired, infollowing time intervals each representing the possible attenuationconditions experimented by the xDSL line in time;

b) for each xDSL line, the minimum attenuation value measured on theline, along both uplink and downlink, should be available;

c) for each xDSL line, the maximum attenuation value measured on theline, along both uplink and downlink, should be available;

d) for each xDSL line, a mean attenuation value, along both uplink anddownlink of the line itself, should be available.

Specifically, this mean value can be obtained as moving average of acertain number of subsequent measures in time. It is advisable that thenumber of measures used in the moving average and their weightcoefficients depend on the frequency with which measures are acquired,in addition to the method used for acquiring and storing said measures,in order to be able to modulate the weight that, when computing themean, the most recently acquired measures have with respect to the olderones.

With reference now to FIG. 3, after having fixed a line to be qualified(block 100 in FIG. 3) belonging for example to a flexible networkportion, the analysis method according to the invention comprises thefollowing steps:

Step 1. Collection of Information Related to the Line to be Qualified(Block 110 in FIG. 3):

in this step cabinet 11 and distribution point 12 associated to theconsidered line are determined; afterwards, all distribution points 12of the broadband type are located, belonging to the cabinet area 13related to cabinet 11 and, for such distribution points 12 of thebroadband type, attenuation measures of the DELT type, related to uplinkand downlink of xDSL lines connected thereto, are recovered from themeasure database 15;

Step 2 Validation and Standardisation of Measures of the DELT Type ofxDSL Lines Located in Step 1 (Block 120 in FIG. 3):

in this step, attenuation measures associated to xDSL lines located inStep 1 are validated through suitable validity checks with the purposeof removing attenuation measures affected by malfunctions of dataacquiring or storing systems. Possible systematic errors on measures,introduced, for example, by specific implementing modes of instrumentsnot complying with international standards are compensated byintroducing corrective factors on measures depending on thecharacterisation in a controlled environment (for example in alaboratory) of the instruments used for measuring the attenuation. Atthe end of this step, the attenuation measures of the DELT typeassociated to xDSL lines located in Step 1 are “standardised”, namelymade mutually uniform.

Step 3. Location of Distribution Points of the Broadband Type Located inStep 1 (block 130 in FIG. 3):

in this step, measures obtained in Step 2 are grouped by distributionpoint of the broadband type to which the measures themselves refer, andthe coherence of such attenuation measures is verified, with the purposeof removing the unreliable attenuation measures, for example due toparticular or atypical subscriber systems, such as those affected by ahigh number of branches as to introduce significant increases on thetotal attenuation experimented by a line with respect to the oneexperimented by the other lines of the same distribution point. At theend of this step, a first location in terms of mean attenuation that canbe associated to distribution points 12 of the broadband type located inStep 1 is performed and a reliability index is assigned to suchlocation. In the present description, the term “location” meansdetermining the mean attenuation value that can be associated with thedistribution point.

Step 4. Discarding the Distribution Points of the Broadband Type Locatedin Positions that are not Coherent with Respect to the Network Modelthat the Operator has (Block 140 in FIG. 3):

in this step, the coherence of the location of individual distributionpoints 12 of the broadband type inside the cabinet area 13 is verifiedwith respect to “typical situations”, namely to homogeneous network andterritory situations (for example urban areas, extra-urban areas), thatcan be associated to the network portion in which such cabinet area isplaced. Specifically, distribution points 12 of the broadband type whoselocation is unreliable as regards characterisation of attenuationdispersion of the cabinet area 13 are discarded. If the line to bequalified is terminated in a distribution point 12 of the broadband typeplaced in a rigid network, the step does not apply.

Step 5. Estimation of Minimum and Maximum Attenuation Dispersion of TheCabinet Area Located in Step 1 (Block 150 in FIG. 3):

the attenuation dispersion is estimated for cabinet area 13 lines,independently whether they are associated to distribution points 12 ofthe broadband type or not, starting from the location performed inprevious steps on broadband distribution points of the cabinet area 13itself. Depending on such attenuation dispersion, minimum and maximumattenuation values can be determined, that can be associated with thecabinet area 13 and form the attenuation range within which measuresobtained on an cabinet area 13 line, on which a xDSL service has to beprovided downstream of its activation, are expected to fall. If the lineto be qualified is terminated in a distribution point 12 of thebroadband type placed in a rigid network, the step does not apply.

Step 6. Estimation of Maximum Bit Rate that can be Offered on the Lineto be Qualified for a xDSL Service (Block 160 in FIG. 3):

depending on minimum and maximum attenuation values obtained in Step 5for the cabinet area 13 to which the line to be qualified belongs and anoise hypothesis associated with the line itself and formed startingfrom:

-   -   the types of services associated to lines (so-called disturbing        lines) that share the same path in the access network with the        line to be qualified and such as to overlap to the spectrum        related to the uplink or downlink of the xDSL service for which        the line is being qualified;    -   the cable cross talk characteristics, that allow evaluating the        portion of signal due to disturbing systems that is translated        into noise on the line being qualified,    -   a bit rate range is estimated, both for the downlink and for the        uplink, within which maximum bit rates can be placed, that can        be obtained on all lines of the affected cabinet area 13, and        therefore also on the line to be qualified, for the xDSL service        that has to be activated. If the line to be qualified is        terminated on a distribution point 12 of the broadband type, the        maximum bit rate that can be obtained on the line itself can be        provided, since it is possible to timely locate such        distribution point.

Herein below in the present description, the above described steps willbe described in more detail.

It is further advisable to state that, during the present description,the term “distance” or “electric distance” means not the physicaldistance at which the individual network elements are placed, but themean attenuation pertaining thereto and that can be seen as consequenceof their position on the territory.

Step 1

Information to be found related to the line to be qualified can beclassified into at least four categories.

Category 1. Information about Network Elements Associated to the Line tobe Qualified:

given a line to be qualified (determined through a univocal identifyingcode, for example the subscriber's telephone number), it is necessary tolocate:

-   -   1) distribution point D_(L) to which the line is jointed;    -   2) cabinet A_(L) to which distribution point D_(L) is connected.        If the line to be qualified crosses many cabinets, cabinet A_(L)        is deemed the one directly connected to distribution point D_(L)        (if the network is of the rigid type, such information is not        necessary);    -   3) the set of distribution points {D_(j)} of the broadband type        connected to cabinet A_(L) (if the network is of a rigid type        such information is not necessary). The absence of distribution        points of the broadband type connected to cabinet A_(L) ends the        analysis method according to the invention;    -   4) the set of xDSL lines {L_(ji)} (where j is the distribution        point index while i points out the i-th broadband line connected        thereto) jointed to distribution points {D_(j)}, including those        jointed to distribution point D_(L) (if the network is of the        rigid type, it is necessary to locate only the xDSL lines        jointed to distribution point D_(L)). If there are no such xDSL        lines, the analysis method according to the invention ends;    -   5) total number N_dp (where dp stands for “distribution point”)        of distribution points (of the broadband type and not) connected        to cabinet A_(L) (if the network is of the rigid type, this        information is not necessary).        Category 2. Attenuation Measures of the DELT Type Related to the        Set of xDSL Lines {Lji}:

provided that conditions a)+e) about acquisition and storage ofattenuation measures are verified, for every xDSL line L_(ji) it isnecessary to find in the measure database 15 the following attenuationmeasures:

-   -   i. Uplink minimum attenuation: Att_min_UP(L_(ji))    -   ii. Uplink mean attenuation: Att_ave_UP(L_(ji))    -   iii. Uplink maximum attenuation: Att_max_UP(L_(ji))    -   iv. Downlink minimum attenuation: Att_min_DN(L_(ji))    -   v. Downlink mean attenuation: Att_ave_DN(L_(ji))    -   vi. Downlink maximum attenuation: Att_max_DN(L_(ji))

The even partial absence of attenuation data for a given xDSL lineL_(ji) brings about the exclusion of such line from the set {L_(ji)}.The exclusion of all xDSL lines L_(ji) from such set instead ends theanalysis method according to the invention.

The lack of reliability of the attenuation measures for one or more xDSLlines L_(ji) is instead managed in Step 2.

Category 3. Type of DSLAM to which Lines {L_(ji)}[DSLAM_T(Lji)] andRelated CPE [CPE_T(Lji)] are Jointed:

this category comprises information related to xDSL technologies used oncentral side (DSLAM) and subscriber side (CPE) for each xDSL lineL_(ji), information that allow distinguishing the DSLAM and CPEmanufacturers to which broadband L_(ji) lines are connected. Suchinformation can be useful for improving the results obtained as outputfrom Step 2. In fact, above all for first generation xDSL systems (theso-called ADSL1) it can be useful to locate possible systematiccorrections to be performed in Step 2 to attenuation measures performedby xDSL equipment receivers supported by each xDSL line L_(ji) andafterwards stored in the measure database 15, depending on theparticular xDSL equipment pair (DSLAM-CPE) associated to the xDSL lineL_(ji) being taken into account, since, for such systems, theattenuation measures are not standardised. This calibration requires aprevious work for detecting, in a controlled environment (for example inlaboratory), possible measure errors performed by various xDSL equipmentpairs (DSLAM-CPE) taking also into account the accuracy in terms ofgranularity with which the attenuation measures are stored both insidethe DSLAM and in the measure database 15. If xDSL systems are deployedin a network certified with respect to attenuation measures execution,information in category 3 are optional.

Category 4. Information for Estimating the Cross Talk Noise:

this category includes all useful information for estimating the crosstalk noise in which the line to be qualified will have to operate.Information of this type can deal for example with: the existence oftransmission systems that can disturb the line to be qualified atpara-cross talk component NEXT level on central receiver side and/or onsubscriber receiver side; the placement of the line to be qualified inthe cable section taken into account with respect to other disturbinglines; cross talk coupling characteristics of subscriber loops placednext to the relevant subscriber loop; the system xDSL system type forwhich the line has to be qualified (SDSL, ADSL, ADSL2+, etc). Generallyinformation belonging to such category are available at Network operatorin one or more network registries related to the network infrastructure1 (for example the database shown in FIG. 1 with number 16).Alternatively, should these information not be available for bothcentral and subscriber side of the line to be qualified, a measure ofthe quiet line noise (as pointed out in ITU-T G.997.1 Recommendation)can be used or a predefined and known noise environment can be assumed,for which it is possible to model the expected network noise so thatmaximum bit rates guaranteed for a xDSL service that have to beestimated depend only on the attenuation.

Step 2

This step subjects attenuation measures related to individual xDSL linesL_(ji) to suitable validity check to detect a possible incongruence dueto malfunctions of xDSL measuring equipment and/or to errors performedwhen storing data. If an incongruence is detected, the xDSL line L_(ji)is discarded or marked with a flag, useful in the following steps of theanalysis method according to the invention.

In addition to validity checks, this step also performs corrections toattenuation measures performed by xDSL equipment realising measures thatare not complying with international standards, such as ITU-T G.997.1(for example first generation ADSL equipment), to compensate forpossible systematic errors associated to these measures. The systematicerrors on attenuation measures detected with non-standard methodsdepend, in general, on the pair of xDSL equipment used on central sideand subscriber side, which can have interoperability problems. Theattenuation measures detected with non-standard methods can becalibrated with measuring campaigns in a controlled environment (forexample in a laboratory). In particular, possible corrections to beperformed to these measures depend on the knowledge both of xDSLtechnology used on DSLAM side [DSLAM_T(Lji)] and on the xDSL technologyused on subscriber modem side [CPE_T(Lji)]. Since often there are nocomplete information about xDSL technologies used by subscriber modemsof each xDSL line Lji, ‘mean’ corrections can be used, depending only onthe xDSL technology on DSLAM side. For first generation ADSL systems,the use of ‘mean’ corrections depending only on the technology on DSLAMside is efficient only for the uplink, while for the downlink itproduces errors that are in practice not acceptable, generally due tothe particular implementing mode of the xDSL modem on subscriber side.

In general, not only for first generation systems such as ADSL1, theattenuation measures related to uplink are more reliable that thoserelated to downlink: in fact the first ones are estimated by thereceiver on DSLAM side and directly stored in the MIB (“ManagementInformation Base”) of the DSLAM itself, while the second ones areestimated by the subscriber modem receiver and relayed to the DSLAMthrough a managing channel at physical level EOC (“Embedded OverheadChannel”). This can imply, especially for technologies of a differenttype on DSLAM side and subscriber modem side, errors and inaccuraciesdue to interoperability problems between equipment. For the same abovedescribed reasons, the attenuation measures used by the analysis methodaccording to the invention are those related to the uplink and possiblecorrections to be performed deal only with these measures. However, forall checks described below, both attenuation measures related to uplinkand those related to downlink are subjected to validation procedures,since also information obtained by the attenuation measures related tothe downlink are used in particular cases that will be described relatedto Step 3 of the analysis method according to the invention.

The corrections of the attenuation measures related to uplink can beperformed by summing the mean attenuation value associated with theuplink of the xDSL line L_(ji) and an additional attenuation value,designated as P(Att_ave_UP(Lji)), where P(x) is a polynomial withvariable order that can depend on the DSLAM and CPE types to which thexDSL line L_(ji) is jointed. The mean attenuation on the uplink is thengiven by Att_ave_UP(L_(ji))=Att_ave_UP(L_(ji))+P(Att_ave_UP(L_(ji)))

The validation of the attenuation measures aims to verify that nocontradictions exist in the set of measures collected for the same lineand generally occurs through three types of validity checks: rangecheck, variability check and coherence check.

Specifically, the range check verifies that the measured attenuationvalues fall within ‘physically’ meaningful ranges with respect tonetwork conditions. In case of ADSL systems, the following can forexample be imposed:

-   -   constraints on minimum attenuations: for example, both for the        attenuation value on the uplink and for the one on the downlink,        no values lower than 1 dB are allowable. This because the link        between permutator 9 and DSLAM 10 typically implies an        attenuation of signals crossing it that is greater than such        value.    -   constraints on maximum attenuations: for example, for the        attenuation values on the uplink, no values greater than 50 dB        are allowable, since greater values would be associated to such        electric distances as not to allow using not only the xDSL        service, but also the traditional telephone service. Other        constraints on maximum attenuations can instead be due to upper        limits imposed by network apparatus (DSLAM, CPE etc) that        perform both the measure and its related storage of attenuation        values.

The variability check verified that in time no significant variationsoccurred on attenuation values measured along xDSL lines L_(ji). Inorder to perform such check, constraints are imposed on the differencebetween maximum and minimum values of attenuations related to the uplinkand downlink of said lines. With the same line wiring (number oflengths/cable types/diameters etc.), the difference between maximum andminimum attenuation values in time is caused only by thermal variationsthat are relatively low (for example less than about 1 dB). However,even in this case it is advisable to take into account the accuracy withwhich the measuring xDSL equipment store values measured thereby: forexample, some DSLAM (old generation type) store only integer values ofmeasured ADSL attenuation values. In this case, it is preferable toincrease the width of the variability range allowed for the differencebetween maximum and minimum attenuation values (an acceptable value forsuch range could be for example 2 dB).

Finally, the coherence check verifies that the relationship betweenattenuation values related to the uplink and downlink of a same xDSLline has a ‘physically’ reasonable value. For example, given thespectrum allocations dedicated to transmissions for the uplink anddownlink, it would be not admissible, for a signal of the ADSL type, tohave an attenuation value on the downlink that is less than the onedetected on the uplink, while, for a signal of the SDSL type, therelationship between the two attenuation values should practically be aunit. In general, the relationship between attenuation values related tothe uplink and downlink of a same xDSL line L_(ji) depends on the typeof cable in which the line is comprised, and is particularly sensitiveto the diameter of the copper pairs container in said cable (in systemssuch as the first generation ADSL, it can also depend on the bit ratesat which the line is operating on the respective uplink and downlink).The Network operator, depending on the knowledge of cables used in itsown network and on tolerances included in the attenuation measuresperformed by its own xDSL equipment, can previously characterise thelimits within which the attenuation values relationship can becontained.

If for a line L_(ji) only one of range and/or variability checks is notobserved, the line and its related attenuation measures are discardedfrom the set {L_(ji)}. If instead range and variability checks arepassed, while the coherence check is not, the line will be marked with aflag that will be used in Step 3 without any other evaluation criteriaof the quality of measures associated with the line itself. The reasonfor this different importance assigned to the above described types ofcheck is that, for first generation ADSL systems, the attenuationmeasure related to the downlink is in general scarcely reliable and thiscan strongly impair the values obtained for the relationship betweenattenuations and therefore the results produced by the coherence check.In particular, for all lines that passed the range and variabilitychecks, it is possible to go on giving a value to logic variableFlag_Atn(L_(ji)) equal for example to 1 if the relationship ofattenuation values related to the downlink and uplink of the above linescomplies with the previously located limits or equal to 0 otherwise.

Concluding, at the end of this step, every line L_(ji) that has passedthe range and variability checks will be characterised by the meanattenuation value associated with its uplink Att_ave_UP(L_(ji)),possibly corrected by the additional value P(Att_ave_UP(Lji)) and thelogic variable Flag_Atn(L_(ji)), associated with the coherence checkresult.

Step 3

In this step, initially the mean attenuation value is estimated on theuplink related to each one of the distribution points of the broadbandtype of the set {D_(j)} to which the xDSL lines L_(ji) are jointed. Inparticular, such mean attenuation value is computed starting from themean attenuation values related to the uplink of the above xDSL linesL_(ji). Specifically, the estimation is performed on all distributionpoints of the broadband type {D_(j)} equipped with validated measures ofthe DELT type and is equipped with additional information related to itsreliability. The main concept used for estimating the mean attenuationvalue to the single distribution point of the broadband type D_(j) ishaving a certain degree of coherence between attenuation measuresassociated with all lines jointed to such distribution point: thisbecause it is assumed that lines of a same distribution point mutuallyhave attenuation measures with reduced dispersion, since, belonging to asame condominium or to different living buildings grouped in a verynarrow geographical area, they share the same path in the access network2 between central and distribution point.

The location of distribution points of the broadband type {D_(j)} in theaccess network 2 is therefore based on the estimation of the meanattenuation value of various distribution points. Due to many factors,for example the excessive dispersion of available attenuation measureson the same distribution point, such location can however be unreliableor even not able to be actuated. Therefore, at the end of this step, thedistribution points of the broadband type D_(j) associated to xDSL linesL_(ji) will be classified into one of the following categories:

-   -   Distribution points of the G type (Guide distribution point):        distribution points for which the location has to be considered        certain, since the mean attenuation value estimated for them is        reliable;    -   Distribution points of the A type (Ambiguous distribution        point): in this case, the location of the distribution points        cannot be considered certain and will be the object of further        evaluations in the following step of the analysis method since        the estimated mean attenuation value for these distribution        points is only “relatively” reliable;    -   Distribution points of the D type (Discarded distribution        point): distribution points that are discarded due to the lack        of correlation between attenuation measures associated with xDSL        lines L_(ji) jointed thereto.

More particularly, FIG. 4 shows a possible flow diagram related to step3, as it is applied on a generic distribution point of the broadbandtype D_(j) equipped with |L_(ji)| validated measures of the DELT type(block 200 in FIG. 4).

Always referring to FIG. 4, it occurs that if to the distribution pointof the broadband type D_(j) only one xDSL line is jointed to validatedmeasures of the DELT type, namely |L_(ji)| is equal to 1, (block 210 inFIG. 4). If this is the case, it is not possible to verify whether thereis a certain degree of coherence between attenuation measures associatedto many xDSL lines {L_(ji)}; therefore, in order to decide whether it issuitable to locate the distribution point of the broadband type D_(j)depending on the single xDSL line L_(ji) jointed thereto, the coherenceis checked (block 220 in FIG. 4) between attenuation values on theuplink and downlink of the available line, namely it is checked whetherlogic variable Flag_Atn associated with the xDSL line L_(ji) is, forexample, equal to 1 (value for which there is coherence in therelationship between attenuations related to the downlink and uplink ofthe line). If this condition is verified, the distribution point of thebroadband type D_(j) is assigned the mean attenuation value on theuplink of its own xDSL line L_(ji) and the distribution point of thebroadband type D_(j) is classified with type A, namely the performedestimation is not deemed completely reliable (block 230 in FIG. 4). Nowthe location procedure of the generic distribution point of thebroadband type D_(j) ends (block 240 in FIG. 4). If instead logicvariable Flag_Atn is, for example, equal to zero, the distribution pointof the broadband type D_(j) is classified as type D and no attenuationvalue is assigned thereto (block 250 in FIG. 4); the location procedureof the generic distribution point of the broadband type D_(j) thereforeends (block 240 in FIG. 4).

Let us now consider the general case in which, to the distribution pointof the broadband type D_(j) two or more xDSL lines {L_(ji)} are jointedwith validated measures of the DELT type, namely |L_(ji)|>1.Preliminarily, it is important to establish a condition related to themaximum attenuation dispersion parameter (Max_Disp_DP) that can beassociated with the distribution point D_(j), meaning as attenuationdispersion the difference between maximum attenuation value and minimumattenuation value related to the uplink of the set of xDSL lines{L_(ji)} jointed to the distribution point. The above cited condition isestablished assuming that, since the set of xDSL lines {L_(ji)} jointedto the same distribution point has shared in a network the majority ofthe path, what can differentiate their attenuation value is only thesubscriber loop joining the distribution point with the subscriberequipment (xDSL modem).

In order to establish the maximum attenuation dispersion parameterMax_Disp_DP it is advisable to have the following information available:

-   -   typical structure of living buildings of the portion of        territory served by the Operator's access network (typically a        portion of territory characterised by living models based on        palaces will have a greater attenuation dispersion with respect        to an urban area based on single-family houses (for example the        xDSL lines of a sky-scraper will have more widespread        attenuation values given the nature itself of the living        structure);    -   main types and characteristics (cable type, diameter,        insulation, etc.) of subscriber loops;    -   attenuation value typically introduced by a medium-quality        subscriber system.

Moreover, in order to establish the maximum attenuation dispersionparameter Max_Disp_DP, it is important to take into account also thetolerances related to measuring methods used by xDSL equipment, theaccuracy of systems for storing such measures and the attenuationvariations due to thermal effects.

As an example, a reasonable value in a urban area for the maximumattenuation dispersion parameter Max_Disp_DP, if attenuation measuresperformed by ADSL1 equipment are used, can be on the order of 4 dB.

With reference again to FIG. 4, after having fixed a value for themaximum attenuation dispersion parameter Max_Disp_DP, Step 3 of theanalysis method according to the invention provides for the following.

For every distribution point of the broadband type D_(j) with a numberof xDSL lines {L_(ji)} greater than 1, in a vector Att_ave_UP, valuesAtt_ave_UP(L_(ji)) of available attenuation measures for each uplink ofthe above lines are ordered in an ascending way, and their dispersionvalue (Disp_DP) is evaluated:Disp_DP=max_(i)(Att_ave_UP(L _(ji)))−min_(i)(Att_ave_UP(L _(ji)))(block 260 in FIG. 4). This value is then compared with the previouslyset maximum attenuation dispersion parameter (Max_Disp_DP) (block 270 inFIG. 4).

If the attenuation dispersion value (Disp_DP) on the distribution pointof the broadband type D_(j) is lower that the maximum established oneDisp_DP<Max_Disp_DP (line 20 in FIG. 4), then it is possible to assignto the distribution point a mean attenuation value for the uplink with ahigh reliability degree, so that:

-   -   the distribution point of the broadband type D_(j) is classified        as belonging to category G (DP_type(D_(j))=G)    -   the relative mean attenuation value for the uplink Atn_DP(D_(j))        is the arithmetic mean of mean attenuation values for the uplink        related to the xDSL lines {L_(ji)} jointed to the distribution        point itself

$\left( {{{Atn\_ DP}\left( D_{j} \right)} = {\frac{1}{L_{ji}} \cdot {\sum\limits_{i}{{Att\_ ave}{\_ UP}\left( L_{ji} \right)}}}} \right)$(block 280 in FIG. 4).

Now the location procedure of the generic distribution point of thebroadband type D_(j) ends (block 290 in FIG. 4).

If instead the attenuation dispersion value (Disp_DP) on thedistribution point of the broadband type D_(j) is greater than thepreviously fixed maximum attenuation dispersion parameter (Max_Disp_DP),namely Disp_DP≧Max_Disp_DP (line 30 in FIG. 4), the analysis methodaccording to the invention provides that the attenuation measures thatare unrelated with respect to the set of measures |L_(ji)| related toxDSL lines L_(ji) jointed to the distribution point are located anddiscarded.

In particular, two cases can be distinguished, according to the numberof xDSL lines {L_(ji)} with validated measures of the DELT type:|L_(ji)|=2 e|L_(ji)|>2.

If only two xDSL lines L_(ji) with validated measures of the DELT typeare jointed to the distribution point, namely |L_(ji)|=2, (block 300 inFIG. 4), it is not possible to establish from a simple comparison ofmeasures which between the two attenuation values associated with theuplink of the two xDSL lines L_(ji) can be discarded; in this case, theanalysis method according to the invention provides that, between thetwo xDSL lines L_(ji) available, only the one that has coherence betweenmean attenuation values for its own uplink and downlink (namelyFlag_Atn(L_(ji))=1) is taken into account. In particular the followingis valid.

-   -   if none of the two xDSL lines L_(ji) has a coherence between        mean attenuation values for the respective uplink and downlink,        namely Flag_Atn(L_(ji))=0 for both lines, the distribution point        is classified of the D type (DP_type(D_(j))=D) ad no attenuation        value is assigned thereto Atn_DP(D_(j))=‘-’ (block 320 in FIG.        4); now the location procedure of the generic distribution point        of the broadband type D_(j) ends (block 330 in FIG. 4).    -   if only one among the xDSL lines L_(ji) jointed to the        distribution point of the broadband type D_(j) has a coherence        between mean attenuation values for the respective uplink and        downlink, namely Flag_Atn=1, then the mean attenuation value        assigned to the distribution point is equal to the mean        attenuation value for the uplink related to such line        (Atn_DP(D_(j))=Att_ave_UP (L_(ji)) and the distribution point is        classified of type A (DP_type(D_(j))=A) (block 340 in FIG. 4);        now the location procedure of the generic distribution point of        the broadband type D_(j) ends (block 330 in FIG. 4).    -   if both xDSL lines {L_(ji)} jointed to the distribution point of        the broadband type D_(j) have a coherence between respective        mean attenuation values for uplink and downlink, namely        Flag_Atn=1 for both lines, then the mean attenuation value        assigned to the distribution point is equal to the arithmetic        mean of the attenuation values for the uplink of both lines

$\left( {{{Atn\_ DP}\left( D_{j} \right)} = {\frac{1}{2} \cdot {\sum\limits_{i = 1}^{2}{{Att\_ ave}{\_ UP}\left( L_{ij} \right)}}}} \right)$and the distribution point is classified as type A (DP_type(D_(j))=A)(block 350 in FIG. 4); now the location procedure of the genericdistribution point of the broadband type D_(j) ends (block 330 in FIG.4).

If instead to the distribution point of the broadband type D_(j) anumber of xDSL lines {L_(ji)} is jointed with validated measures of theDELT type greater than 2, namely |L_(ji)|>2, always supposing that theattenuation dispersion value (Disp_DP) on the distribution point of thebroadband type D_(j) is greater than the previously used maximumattenuation dispersion parameter, namely Disp_DP≧Max_Disp_DP, (block 310in FIG. 4), it is attempted to locate and discard the xDSL lines{L_(ji)} responsible for the excessive attenuation dispersion (Disp_DP)in order to reduce this latter one below the maximum attenuationdispersion parameter Max_Disp_DP. Such lines are those with which theattenuation values are associated:

-   -   max_(i)(Att_ave_UP(L_(ji))), namely Att_ave_UP(|L_(ji)|)    -   min_(i)(Att_ave_UP(L_(ji))), namely Att_ave_UP(1).

where the position of such values in vector Att_ave_UP depends on thechosen ordering for realising such vector (block 260 in FIG. 4). Suchvalues are removed from vector Att_ave_UP if it happens for them thelack of correlation with respect to the other attenuation measuresavailable for each uplink related to the distribution point D_(j). Inparticular, the Att_ave_UP(|L_(ji)|) value is deemed uncorrelated andtherefore removed from vector Att_ave_UP if it is different from theattenuation measure nearest thereto (Att_ave_UP(|L_(ji)|−1)) by morethan a fixed threshold (Thr_DP); while value Att_ave_UP(1) is deemeduncorrelated and therefore removed from vector Att_ave_UP if it isdifferent from the attenuation measure nearest thereto (Att_ave_UP(2))by more than a fixed threshold (Thr_DP)

The location of uncorrelated elements present in vector Att_ave_UP isapplied iteratively, keeping track upon every iteration of how manyvalues have been removed (consequently reviewing value |L_(ji)| everytime) and again evaluating the attenuation dispersion value (Disp_DP) onthe distribution point of the broadband type D_(j).

Downstream of every single iteration, the procedure described in block310 continues to be iterated if the result of the previously endediteration has produced a removal from vector Att_ave_UP, the number ofvalues still present in vector Att_ave_UP is greater than 2 and theattenuation values dispersion is still greater than the fixed maximumattenuation dispersion parameter.

If the iteration of block 310 in FIG. 4 ends, the following cases canoccur

-   -   the attenuation dispersion value (Disp_DP) on the distribution        point of the broadband type D_(j) has been reduced below the        maximum allowed value, namely Disp_DP<Max_Disp_DP (line 40 in        FIG. 4). In this case (block 360 in FIG. 4) the distribution        point of the broadband type D_(j) is classified of the G type        (DP_type(D_(j))=G); the related mean attenuation value for the        uplink Atn_DP(D_(j)) is the arithmetic mean of mean attenuation        values for the uplink related to xDSL lines {L_(ji)} jointed to        the distribution point itself and still available downstream of        discards produced in block 310

$\left( {{{Atn\_ DP}\left( D_{j} \right)} = {\frac{1}{L_{ji}} \cdot {\sum\limits_{i}{{Att\_ ave}{\_ UP}\left( L_{ji} \right)}}}} \right).$Now the location procedure of the generic distribution point of thebroadband type D_(j) ends (block 370 in FIG. 4).

-   -   the attenuation dispersion value (Disp_DP) on the distribution        point of the broadband type D_(j) has not been reduced below the        maximum allowed value, namely Disp_DP≧Max_Disp_DP (line 50 in        FIG. 4) and on the distribution point, downstream of discards        performed in block 310, only two xDSL lines L_(ji) are available        with validated measures of the DELT type. In this case, the        location procedure of the generic distribution point of the        broadband type D_(j) provides that the same steps previously        described and contained in blocks 300-320-330-340-350 in FIG. 4,        are performed;    -   the attenuation dispersion value (Disp_DP) on the distribution        point of the broadband type D_(j) has not been reduced below the        fixed maximum attenuation dispersion parameter, namely        Disp_DP≧Max_Disp_DP (line 60 in FIG. 4) and at the distribution        point, downstream of discards performed in block 310, more than        two xDSL lines L_(ji) are available with validated measures of        the DELT type. In this case the mean square deviation (σ) of        |L_(ji)| mean attenuation measures media related to the uplink        is evaluated (block 380 in FIG. 4) and this is compared with a        prefixed threshold (Thr_σ).    -   If (block 390 in FIG. 4) the mean square deviation (σ) is lower        than the threshold Thr_σ (σ≦Thr_σ), then the location procedure        provides that the same previously described steps are performed,        that are contained in blocks 360 and 370 in FIG. 4;    -   If (block 400 in FIG. 4) the mean square deviation (σ) is        greater than the threshold Thr_σ (σ≧Thr_σ), then the        distribution point of the broadband type D_(j) is classified of        the D type and no attenuation value is assigned thereto (block        410 in FIG. 4); the location procedure of the generic        distribution point of the broadband type D_(j) then ends (block        420 in FIG. 4).

As regards the threshold value Thr_DP, it is a factor that depends onnetwork topology. Such factor can be calibrated depending on the sameparameters that brought about the definition of maximum attenuationdispersion parameter Max_Disp_DP, this time do not taking into accountthe xDSL lines of a whole living unit but, for example, only thosebelonging to contiguous floors. An acceptable threshold value in anetwork where there is typically one distribution point per palace isabout 2 dB.

As regards the choice of the threshold value Thr_σ, this latter one is afactor that can be obtained depending on the fixed value for the maximumattenuation dispersion parameter Max_Disp_DP evaluating the mean squaredeviation that is realised on the distribution points of the broadbandtype with more than two xDSL lines L_(ji) mutually jointed withvalidated measures of the DELT type and with Disp_DP<Max_Disp_DP.

At the end of previously described Step 3, it can be deemed that acertain number of distribution points of the broadband type D_(j) hasbeen located through vector Atn_DP, some of which in an assured way(distribution points of the G type), other in an unassured way(distribution points of the A type), through vector DP_type; the otherdistribution points (distribution points discarded or of the D type)will not be taken into account any more in the following steps of theanalysis method according to the invention.

Step 4

This step evaluates, for cabinet area A_(L) to which the line to bequalified is jointed, the maximum and minimum attenuation values of thedistribution points of the broadband type D_(j) related thereto. Infact, it has to be noted that, though in Step 3 a first location ofthese distribution points has been performed, for the distributionpoints of the broadband type D_(j) classified as of type A such locationis not yet assured.

Since that, due to the variability of subscriber systems, it is muchmore probable to perform an over-estimation of the attenuation relatedto a distribution point than an under-estimation, since subscribersystems, being often of a low quality, can introduce an additionalattenuation component, the major problem is the distinction betweencases of distribution points classified as of type A actually remotefrom the exchange with respect to those wrongly located as remote due toa low-quality subscriber system. Distinguishing between these two casesmeans recognising the cases of a secondary networks actually wide spreadwith respect to cases in which the secondary network wrongly appearsmuch spread due to attenuation over-estimations.

The problem is dealt with by evaluating the degree of coherence of thelocation of distribution points of the broadband type Dj being part ofthe cabinet area A_(L) with respect to ‘typical situations’, linked tohomogeneous network and territory situations (for example urban areas,extra-urban areas), that can occur in the network portion in which suchcabinet area is placed. Such ‘typical situations’ are identified througha parameter Max_Disp_Cab that represents the maximum attenuationdispersion allows on the cabinet areas of the considered networkportion, whose knowledge can be obtained with one of the proceduresdescribed below:

-   -   procedure 1) cabinet areas are taken into account, that are        present in the considered network portion, that have their        distribution point remotest from the central (namely the one        with highest attenuation) classified of the G type, and,        depending on these, the Cumulative Distribution Function is        evaluated for the difference between maximum value and minimum        value of attenuations associated with such distribution points        of the G type cabinet by cabinet, namely the cumulative        distribution of the attenuation dispersion parameter        Disp_(k)=max_(j) (Atn_DP(D_(jk)))−min_(j)(Atn_DP(D_(jk)) is        computed, where Disp_(k) represents the dispersion in terms of        attenuation of the k-th cabinet area of the considered network        portion. As regards the analysis method according to the        invention, the parameter Max_Disp_Cab is the 90-th percent        (“quantile”) of such distribution. The choice of the 90-th        percent is not constraining, but in analyses performed for        defining the analysis method according to the invention, this        was the value that allowed obtaining the best results.        Procedure 1) supposes that the relevant cumulative distribution        be statistically significant with respect to the considered        network portion, namely that it has been possible to locate        inside the above network portion many cabinet areas where the        distribution point with the highest attenuation value is of the        G type;    -   procedure 2) topologic knowledge are exploited beforehand on the        network, such as to make it possible to choose Max_Disp_Cab;    -   procedure 3) it is an iterative procedure that will be described        below.

Specifically, in Step 4, the analysis method according to the inventionprovides for previously ordering the attenuation values related tovarious distribution points of the broadband type D_(j) of the cabinetarea A_(L) in an increasing order and to take into account a maximumlimit Thr_cab between two consecutive attenuation values.

The value to be imposed to the maximum limit Thr_cab can changeaccording to the considered network portion, as well as the valueobtained for parameter Max_Disp_Cab can change. In particular, the valueto be imposed to the maximum limit Thr_cab is obtained as follows:Thr_cab=k*Max_Disp_Cab/(R−1)

where k is a corrective factor that takes into account the mean distancebetween two consecutive distribution points of the broadband type D_(j)given by:

$k = {\sum\limits_{i = 1}^{R - S + 1}{{\mathbb{i}} \cdot \left( {\sum\limits_{j = 1}^{R - i - S + 2}\frac{\begin{pmatrix}{R - {\mathbb{i}} - j} \\{S - 2}\end{pmatrix}}{\begin{pmatrix}R \\S\end{pmatrix}}} \right)}}$where R is the mean number of distribution points of the broadband typeD_(j) of the cabinet areas of the considered network portion, S is themean number of distribution points of the broadband type D_(j) locatedin Step 3, both of the G type and of the A type, for the cabinet areasof the considered network portion (it will be S≦R).

After having established the values of parameter Max_Disp_Cab andmaximum limit Thr_cab, Step 4 of the analysis method according to theinvention will now be described with reference to the flow diagram shownin FIG. 5.

Step 4 has as inputs vectors Atn_DP(D_(j)) and DP_type(D_(j)) related tocabinet area A_(L) (block 500 in FIG. 5). Vectors Atn_DP(D_(j)) andDP_type(D_(j)) represent, respectively, the attenuation value assignedto the generic distribution point of the broadband type Dj and the typeof classification assigned to the same distribution point. Index j of Djchanges in order to identify only the distribution points of the G typeand the A type remained after Step 3. Vector Atn_DP(D_(j)) should beordered in an ascending way, reviewing in a congruent way also thepositions of elements of vector DP_type(D_(j)).

Always with reference to FIG. 5, it is checked whether in cabinet areaA_(L) there is a single distribution point of the broadband type D_(j)(independently whether of the A type or of the G type), namely |D_(J)|=1(block 510 in FIG. 5). If this is the case, (block 520 in FIG. 5) thearea is discarded since it is not possible to estimate an interval ofattenuations from the single available attenuation value. Now theanalysis method for a line to be qualified that belongs to a cabinetarea A_(L) of such kind is interrupted without providing results (block530 in FIG. 5).

If instead in the cabinet area A_(L) there are two or more distributionpoints of the A or G type, namely |D_(J)|>1 (line 70 in FIG. 5) thedispersion Disp_Cab=max_(j)(Atn_DP(D_(j)))−min_(j)(Atn_DP(D_(j))) of thecabinet area A_(L) is evaluated and is compared with the maximum alloweddispersion Max_Disp_Cab (block 540 in FIG. 5).

If Disp_Cab<Max_Disp_Cab or the last distribution point (namely the onethat has the highest attenuation value) of the cabinet area A_(L) hasbeen located in a reliable way (DP_type(|D_(j)|)=G) (block 550 in FIG.5), then it is assumed (block 560 in FIG. 5):

-   -   as minimum attenuation value related to the cabinet area A_(L),        the minimum value of the distribution points related to the        above area, namely Min_Cab=min_(j)(Atn_DP(D_(j))), independently        whether such minimum attenuation value is related to a        distribution point of the A type or the G type, this because, as        already stated, attenuation under-estimations are rare;    -   As maximum attenuation value related to the cabinet area A_(L),        the maximum attenuation value of the distribution points related        to the above area, namely Max_Cab=max_(j)(Atn_DP(D_(j)));    -   As mean attenuation value related to the cabinet area A_(L), the        mean of attenuation values of the distribution points related to        the above area, namely

${Avg\_ Cab} = {\frac{1}{D_{j}} \cdot {\sum\limits_{j}{{ATN\_ DP}\left( D_{j} \right)}}}$The distribution points discard procedure then ends (block 570 in FIG.5).

If instead the last distribution point of the cabinet area A_(L) is oftype A (DP_type(D_(j))=G) or the cabinet area dispersion is greater thanthe maximum allowed one (Disp_Cab≧Max_Disp_Cab) (line 80 in FIG. 5)different cases are provided:

-   -   A) if for the cabinet area A_(L) only two distribution points        remained (|D_(j)|=2) (block 580 in FIG. 5), it is not possible        to reliably evaluate the extension of secondary network and        cabinet A_(L) is discarded. The analysis method according to the        invention for qualifying a line that belongs to a cabinet area        A_(L) of such kind is then interrupted without providing results        (block 590 in FIG. 5);    -   B) if the number of distribution points of the broadband type        D_(j) is greater than 2 (|D_(j)|>2) (block 600 in FIG. 5),        iteratively in block 610 the distribution point with highest        attenuation value is removed (namely the “remotest” one        Atn_DP(|D_(j)|)) if its attenuation value is far from the        immediately previous one Atn_DP(|D_(j-)|−1) more than Thr_cab.        Upon every iteration, Disp_Cab is re-computed and some mutually        exclusive conditions must occur, that determine output from        block 610, namely:        -   B1) if downstream of every iteration of block 610, on the            cabinet area A_(L) there is Disp_Cab<Max_Disp_Cab or the            last distribution point of the cabinet area A_(L) is of the            G type (block 620 in FIG. 5), the procedure provides for            re-applying the same previously described decisions related            to blocks 560 and 570 in FIG. 5;        -   B2) if downstream of every iteration of block 610, on the            cabinet area A_(L) only two distribution points of the            broadband type are available (|D_(j)|=2) (block 630 in FIG.            5), in this case it is not possible to reliably evaluate the            extension of secondary network and cabinet A_(L) is            discarded. The analysis method according to the invention            for qualifying a line that belongs to a cabinet area A_(L)            of such kind is then interrupted without providing results            (block 640 in FIG. 5);        -   B3) if downstream of every iteration of block 610, the last            two distribution points of the broadband type D_(j) of the            ordered set differ as attenuation by less than Thr_cab            (block 650 in FIG. 5) then, in this case, if the            last-but-one distribution point is of the G type (block 660            in FIG. 5), in the set of distribution points of the            broadband type {Dj} both last and last-but-one distribution            points are kept and the same, previously described decisions            are applied again, related to blocks 560 and 570 in FIG. 5.            If instead also the last-but-one distribution point of the            broadband type D_(j) is of the A type (block 670 in FIG. 5),            the offset Δ is evaluated between “last-but-one” and            “last-but-two” distribution points. In fact, it is deemed            that the presence of three distribution points with            attenuation measures that are not strongly uncorrelated            apart from the respective classification category is a            sufficient condition for deeming the attenuation measures            related thereto as reliable: therefore, if Δ<Thr_cab (block            680 in FIG. 5) all three distribution points are kept in the            set of distribution points of the broadband type {Dj} and            the same previously described decisions are applied again,            related to blocks 560 and 570 in FIG. 5. Vice versa, if            Δ>Thr_cab, (block 690 in FIG. 5) last and last-but-one            distribution points are discarded from the set of            distribution points of the broadband type {Dj}. In this            latter case:            -   if two distribution points remain in the set (block 700                in FIG. 5) and for such distribution points                Disp_Cab<Max_Disp_Cab or the last distribution point of                the cabinet area A_(L) is of the G type (block 710 in                FIG. 5), the same previously described decisions are                applied again, related to blocks 560 and 570 in FIG. 5.                If instead there is a greater dispersion that the                maximum allowed one or there is a last distribution                point of the A type (block 720 in FIG. 5), it is not                possible to reliably evaluate the extension of the                secondary network and cabinet A_(L) is discarded. The                analysis method according to the invention for                qualifying a line that belongs to a cabinet area A_(L)                of such kind is then interrupted without providing                results (block 730 in FIG. 5)            -   if a single distribution point remains (namely, there                were three distribution points before the removal)                (block 740 in FIG. 5), it is not possible to reliably                evaluate the extension of the secondary network and                cabinet A_(L) is discarded. The analysis method                according to the invention for qualifying a line that                belongs to a cabinet area A_(L) of such kind is then                interrupted without providing results (block 750 in FIG.                5)            -   if instead there remain more than two distribution                points (block 760 in FIG. 5), then the same previously                described decisions are applied again, related to blocks                560 and 570 in FIG. 5.

At the end of Step 4, for cabinet A_(L) to which the line to bequalified is jointed, the following values will be available:

-   -   minimum attenuation Min_Cab=min_(j)(Atn_DP(D_(J)));    -   maximum attenuation Max_Cab=max_(j)(Atn_DP(D_(J)));

${{mean}\mspace{14mu}{attenuation}\mspace{14mu}{Avg\_ Cab}} = {\frac{1}{D_{j}} \cdot {\sum\limits_{j}{{ATN\_ DP}\left( D_{j} \right)}}}$

The results of the above described Step 4 can be affected by the choiceof parameter Max_Disp_Cab. In order to make such choice more accurate,the iterative procedure can be used, previously designated as procedure3, and described below:

-   -   1. the whole above described Step 4 is performed a first time on        all cabinet areas of the considered network portion, using an        attempt value of Max_Disp_Cab (for example the one estimated        through procedure 1), even if obtained from a statistically        scarcely significant sample of distribution points of the G        type).    -   2. downstream of this, the cumulative distribution of        attenuation dispersion parameter Disp_(k)=max_(j)        (Atn_DP(D_(jk)))−min_(j)(Atn_DP(D_(jk)), where Disp_(k)        represents the dispersion in terms of attenuation of the k-th        cabinet area. The 90-th percent of the above computed        distribution is considered as new value of parameter        Max_Disp_Cab and Step 4 is applied again starting from original        data.    -   3. the above described procedure is repeatedly applied, till the        cumulative distributions obtained from two consecutive        iterations has neglectable differences, this meaning that the        procedure has come to a convergence. As final value to be        applied to parameter Max_Disp_Cab, the 90-th percent related to        the cumulative distribution obtained in the last iteration is        used.        Step 5

At the end of Step 4, for the cabinet area A_(L) to which the line to bequalified belongs, a range of attenuation values (included in rangeMin_Cab÷Max_Cab) is anyway available, obtained depending on distributionpoints of the broadband type D_(j) with validated measures associatedwith the above cabinet area A_(L): such distribution points are only asubset of the set of distribution points of the broadband type belongingto the considered cabinet area.

Purpose of Step 5 is performing an estimation of the range ofattenuations of the whole cabinet area A_(L).

If in the previous step for estimating the attenuation dispersion of thecabinet area A_(L), defined as Disp_cab=Max_Cab−Min_Cab, only |D_(j)|distribution points of the broadband type have been used on N_dpdistribution points present in the cabinet area itself, a betterestimation of this dispersion, herein below defined as New_Disp_cab, canbe obtained using the following formula:New_Disp_cab=(N_dp−1)*Disp_cab/h,with

$h = {\sum\limits_{i = {{{Dj}} - 1}}^{{N\_ dp} - 1}{{\mathbb{i}} \cdot \frac{\begin{pmatrix}{{\mathbb{i}} - 1} \\{{D_{j}} - 2}\end{pmatrix}}{\begin{pmatrix}{N\_ dp} \\{D_{j}}\end{pmatrix}} \cdot {\left( {{N\_ dp} - {\mathbb{i}}} \right).}}}$

Parameter h describes the mean of distances, expressed in number ofintervals, between the “remotest” and the “nearest” distribution pointsof the broadband type D_(j) to cabinet A_(L) assuming N_dp distributionpoints at the same distance between them.

After having computed New_Disp_cab, also Min_Cab and Max_Cab valuesshould be modified: in particular, the difference between the newattenuation dispersion value New_Disp_cab and the original valueDisp_cab can be divided on Min_Cab and Max_Cab values proportionallywith respect to the mean of attenuation Avg_Cab. In formulas, havingdefined

${\alpha = \frac{{Max\_ Cab} - {Avg\_ Cab}}{Disp\_ cab}},$the new estimations of Min_Cab and Max_Cab will be:New_Max_Cab=Max_Cab+α·(New_Disp_cab−Disp_cab);New_Min_Cab=max(δ,Min_Cab−(1−α)·(New_Disp_cab−Disp_cab))

-   -   where δ is the value set in step 2 related to the constraint on        minimum attenuations (for example 1 dB). In this way New_Min_Cab        cannot assume values lower than δ, limit below which it is        deemed that an attenuation measure has no physical meaning.        Step 6

Depending on hypotheses associated with the line to be qualifiedobtained taking into account:

-   -   the types of services associated with lines (disturbing lines)        sharing the same access network path with the line to be        qualified and such as to overlap the spectrum related to the        uplink or downlink of the xDSL service for which the line is        being qualified;    -   cable cross talk characteristics, that allow evaluating the        portion of signal due to disturbing systems that can be        translated into noise on the line being qualified,        New_Min_Cab and New_Max_Cab values obtained at the end of Step 5        can be translated into bit rates that can be offered with a        certain xDSL technology on lines belonging to the cabinet area        A_(L) and therefore on the line to be qualified, using for        example the methods for estimating xDSL performance described in        ETSI Specifications related to Spectrum Management (ETSI TR 101        830).

At the end of Step 6, an estimation of the set of bit rates that can beoffered has therefore been obtained, with a certain xDSL technology, onlines belonging to the cabinet area A_(L) and therefore on the line tobe qualified.

Moreover, if the line to be qualified is jointed to one among the|D_(j)| distribution points of the broadband type of the cabinet areaA_(L) still available after having performed Step 5 (namely to adistribution point of the broadband type that is reliably located), theexact bit rate value that can be offered to users jointed to suchdistribution point can be deemed as estimated.

For lines to be qualified belonging to a network of the rigid type,namely characterised by the absence of cabinets, the analysis methodaccording to the invention can be applied using Steps 1, 2, 3 and 6. Infact, through the first three steps, the distribution point of thebroadband type to which the line to be qualified is jointed, is located,while in Step 6 the attenuation value assigned to the distribution pointis translated into a bit rate that can be offered on the line.

The invention claimed is:
 1. A method for analysing status of asubscriber loop belonging to an access network portion of a fixednetwork infrastructure, said subscriber loop not supporting a broadbandservice, said access network portion comprising further subscriberloops, a set of which support broadband services, comprising: collectingattenuation measures associated with said set of subscriber loopssupporting said broadband services, wherein the attenuation measurescomprise attenuation measures of the Dual End Loop Test (DELT) type; andprocessing said attenuation measures to obtain an estimation of amaximum bit rate that can be offered on said subscriber loop to beanalysed, wherein processing comprises validating said attenuationmeasures with a range check, a variability check, and a coherence checkand computing a mean attenuation value.
 2. The method for analysingaccording to claim 1, wherein said attenuation measures are in messagesexchanged between two pieces of terminal equipment respectively placedin a telecommunication central station and in subscriber premises andassociated with said subscriber loops supporting said broadbandservices.
 3. The method for analysing according to claim 2, wherein saidattenuation measures comprise mean time attenuation values related touplink and downlink of said subscriber loops supporting said broadbandservices.
 4. The method for analysing according to claim 3, wherein saidattenuation measures comprise signal attenuation measures and loopattenuation measures.
 5. The method for analysing according to claim 1,wherein processing said attenuation measures comprise: computing themean attenuation value, wherein the mean attenuation value is related tosaid set of subscriber loops supporting said broadband services startingfrom mean time attenuation values associated with each of saidsubscriber loops; and estimating said maximum bit rate value that can beoffered on said subscriber loop to be analysed starting from said meanattenuation value related to said set of subscriber loops supportingsaid broadband services.
 6. The method for analysing according to claim5, wherein said mean time attenuation values are related to the uplinkof said subscriber loops.
 7. The method for analysing according to claim5, wherein estimating said maximum bit rate value that can be offered onsaid subscriber loop to be analysed comprises estimating a noise valueon said subscriber loop to be analysed depending on the followingparameters: types of services associated with the subscriber loops thatshare with the subscriber loop to be analysed the same path in theaccess network; and cable cross talk characteristics that allowevaluating a portion of signal, due to loops that share with thesubscriber loop to be analysed the same path in the access network.
 8. Asystem for analysing status of a subscriber loop belonging to an accessnetwork portion of a fixed network infrastructure, said subscriber loopnot supporting a broadband service, said access network portioncomprising further subscriber loops, a set of which support broadbandservices, comprises: a module capable of being configured for collectingattenuation measures associated with said set of subscriber loopssupporting said broadband services, wherein the attenuation measurescomprise attenuation measures of the Dual End Loop Test (DELT) type; anda module capable of being configured for processing said attenuationmeasures to obtain an estimation of a maximum bit rate that can beoffered on said subscriber loop to be analysed, wherein processingcomprises validating said attenuation measures with a range check, avariability check, and a coherence check and computing a meanattenuation value.
 9. A non-transitory computer-readable medium storinga computer program product comprising codes that, when executed, performthe analysis method according to claim 1.